Fuel injection valves are known in the prior art in different embodiments. Modern fuel injection valves are frequently used in conjunction with storage injection systems which have a pressure accumulator for storing fuel under high pressure. The injectors assigned to the individual combustion chambers of the internal combustion engine are supplied with fuel from this pressure accumulator. The fuel supply is fed to the pressure accumulator by a high-pressure pump. In order to comply with all the requirements regarding their exhaust-gas threshold values, their fuel consumption and their noise levels, etc. today's internal combustion engines need at each engine characteristic point a precisely defined curve of injection quantity over injection time. In the known fuel injection valves, the volume flow through the nozzle orifices at a certain pressure, and consequently the quantity of fuel injected per unit time, is determined by the cross-section which the nozzle needle releases depending on its respective needle lift. At a specified pressure there is therefore for each required flow rate a correspondingly associated, precisely defined nozzle needle lift. Consequently, in order to set a certain volume flow, the nozzle needle would have to be set to a certain lift value. In order to execute a certain shaped injection curve, the nozzle needle would have to be raised within an injection cycle to several precisely defined positions and possibly even lowered again. In today's known fuel injection valves, however, there are only two precisely defined needle positions, namely zero (valve closed) and full lift (valve fully open). Therefore, only two precisely defined flow rates are also possible, namely zero flow rate and maximum flow rate.
Each flow-rate value which lies between these two extremes can always be achieved only approximately, since in the known injection valves the appropriate needle lift can be set only very imprecisely through modulation of the pressure. As this is done, the nozzle needle “rides” on a hydraulic cushion and is thus also subject to the pressure waves and fluctuations present in the nozzle. As a result, however, instead of the necessary, precisely defined needle lift stop for accurately controlling the injection quantity, only an approximate ballistic stopping point of the nozzle needle is produced. This results in approximate, highly scattered and very poorly reproducible injection quantities, which leads to a below-optimum combustion sequence with associated poor results in terms of emissions, noise and fuel consumption.
In the currently known methods for controlling the flow of fuel into the combustion chamber, this flow is always controlled only indirectly, i.e., the control of the nozzle needle is carried out only indirectly via a hydraulic servo-circuit. Here, however, the temporal and quantitative metering of fuel into the combustion chamber depends on very many influencing factors of this servohydraulic system and fluctuates correspondingly widely, which in turn impacts negatively on the quality of combustion in the engine. In particular, digital switching of the servo-valve (open/closed) cannot carry out any precise shaping of the injection characteristics. In particular, in the lower partial-load range, in which the nozzle needle finds itself while injecting between these two extreme positions, the undefined position of the nozzle needle leads to widely varying and non-reproducible injection quantities. The same problem is exhibited by the pump-nozzle systems also known today, since these also open or close the nozzle needle only indirectly by modulating pressure at the shutoff valve.